A steering gear assembly typically comprises a rack and pinion gear system that translates the rotational movement of the pinion into linear movement of the rack. Many modern vehicles include electric power assisted steering, and these gear assemblies utilize dual pinions. One pinion is responsive to steering wheel input, while the other pinion is powered by an electric motor to provide steering assistance or other controlled steering operations.
When the pinions are subject to high torques or quick changes in torque direction, separation forces are generated between the rack and pinion gears. Accordingly, a yoke assembly is typically provided to keep the rack and pinion in engagement. The yoke assembly typically includes a slide bearing that is biased by a spring to press the rack into engagement with the pinion. Unfortunately, as higher and higher pinion torque is generated, which is especially the case with pinions driven by an electric motor, large separation forces are generated. Thus, large spring forces are required to press the yoke and yoke bearing against the rack. However, higher spring forces result in increased friction between the rack and the yoke bearing.
To overcome these deficiencies, roller bearings have been proposed for use as the yoke bearing. While roller bearings allow higher spring forces with lower coefficients of friction between the rack and bearing, these designs are not without their drawbacks. For example, it has been found that the supporting force provided by current yoke roller bearings on the rack are not as robust as the support obtained by slide bearings. Accordingly, there exists a need to provide a steering gear assembly having a yoke bearing which provides robust support to the rack to provide improved engagement of the rack and pinion gears, while maintaining a low coefficient of friction between the rack and yoke bearing.